Freddy Peralta is, without a doubt, the leader of the Brewers’ starting rotation. He is in his eighth major league season, and assuming he makes at least four more starts, this will be his fifth straight year with at least 17 games started. He’s been around, and as the other good homegrown pitchers who came up around him have disappeared due to trade (Corbin Burnes, Josh Hader) or injury (Brandon Woodruff), he has naturally slotted in as the leader of this pitching staff.
But “leader” and “ace” are not necessarily the same. The term ace, itself, is sort of in the eye of the beholder.